Nuclear Theory·nucl-th

Thursday·July 14, 2022

8 papers—5 primary·3 cross-listed

06
[Submitted on 12 Jul 2022] (cross-list from hep-ph)
Generalized parton distributions through universal moment parameterization: zero skewness case
Yuxun Guo🇺🇸 · Xiangdong Ji🇺🇸 · Kyle Shiells🇺🇸
We present a global analysis program for the generalized parton distributions (GPDs) based on conformal moment expansion. We apply the strategy of universal moment parameterization to fit both the collinear parton distribution functions (PDFs) from phenomenology and generalized form factors from lattice calculations, and show that the parameterization is flexible enough to accommodate these constraints. In addition, we can also fit direct lattice calculations of GPDs from large-momentum effective theory. In this work we focus on the analysis of $t$ -dependent PDFs which correspond to GPDs in the $ξ \to 0$ limit. The strategy also applies to the $ξ \neq = 0$ region with extra parameters, and therefore can be fitted to experimental observables in the future. With a demonstrative example of fitted GPDs, we exhibit the quark transverse angular momentum densities of the proton as well as the impact parameter space distributions of quarks in both unpolarized and transversely polarized protons.
Comments:
29 pages, 11 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2207.05768 [pdf]
JHEP(2022)·56 citations
07
[Submitted on 12 Jul 2022] (cross-list from hep-ph)
Temperature and net baryochemical potential dependence of $η / s$ in a hybrid approach
Niklas Götz🇩🇪 · Hannah Elfner🇩🇪
In this work, the qualitative impact of the net baryochemical potential dependence of the shear viscosity to entropy density ratio $η / s$ in hydrodynamical simulations is studied. The effect of a predicted non-constant $η / s$ ( $μ_{B}$ ) is largely unexplored in hydrodynamic simulations. Previous studies focus only on a temperature dependence or even only a constant effective shear viscosity. This work addresses this issue by studying qualitatively the effect of a generalized $η / s$ ( $T, μ_{B}$ ) in the hybrid approach SMASH-vHLLE, composed of the hadronic transport approach SMASH and the (3+1)d viscous hydrodynamic code vHLLE. In order to reduce the bias of the result on the equation of state used in the hydrodynamic part of the model, $η / s$ is parameterized directly in the energy density and net baryon number density. The parameterization takes into account the constraints of matching to the transport coefficients in the hadronic phase, as well as pQCD results. This work compares the impact of the density dependence for different system sizes and energies and compares the observables with experimental results in the RHIC - BES region $s_{N N}$ =7.7 - 39.0 GeV, as the effect of this generalization is especially relevant for intermediate collision energies, for which the system is in equilibrium for a relevant amount of time, but the net baryochemical potential does not vanish. It is shown that the effect of an explicit net baryon number dependence on the elliptic flow is negligible and only relevant in the early stages of the collision. Additionally, we find that the proposed parameterization could be a good proxy for the shear viscosity in the non-equilibrium hadronic transport stage.
Comments:
11 pages, 12 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2207.05778 [pdf]
PRC(2022)·15 citations
08
[Submitted on 13 Jul 2022] (cross-list from hep-ph)
Gluon dipole factorisation for diffractive dijets
E. Iancu🇫🇷 · A.H. Mueller🇺🇸 · D.N. Triantafyllopoulos🇮🇹 · S.Y. Wei🇨🇳
Within the colour dipole picture for deep inelastic scattering at small Bjorken $x$ , we study the production of a pair of relatively hard jets via coherent diffraction. By "relatively hard" we mean that the transverse momenta of the two jets -- the quark ( $q$ ) and the antiquark ( $q ˉ$ ) generated by the decay of the virtual photon -- are much larger than the target saturation momentum $Q_{s} (Y_{P})$ evaluated at the rapidity gap $Y_{P}$ . We argue that the typical final-state configurations are such that the hard $q q ˉ$ dijets are accompanied by a semi-hard gluon jet, with a transverse momentum of the order of $Q_{s} (Y_{P})$ . The presence of this third jet ensures that the scattering is strong and thus avoids the strong suppression of exclusive (hard) dijet production due to colour transparency. For such "2+1" jet configurations, we demonstrate that both the emission of the semi-hard gluon and its scattering with the hadronic target can be factorised in terms of an effective gluon-gluon dipole. This effective description, originally proposed in [1-4], builds a bridge between the colour dipole picture and collinear factorisation: the cross-section for diffractive 2+1 jets can be written as the product between a hard factor describing the $q q ˉ$ dijets and a semi-hard factor expressing the unintegrated gluon distribution of the Pomeron. The latter is controlled by gluon dipole scattering in the black disk limit and hence is strongly sensitive to gluon saturation. By integrating out the kinematics of the 3 jets, we obtain the $q q ˉ g$ contribution to the diffractive structure function in collinearly-factorised form.
Comments:
58 pages, 16 figures, 3 appendices
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2207.06268 [pdf]
JHEP(2022)·42 citations

Affiliations

first authorsco-authorsvia INSPIRE

Generalized parton distributions through universal moment parameterization: zero skewness case

Temperature and net baryochemical potential dependence of η/s in a hybrid approach

Gluon dipole factorisation for diffractive dijets

Affiliations

Temperature and net baryochemical potential dependence of $η / s$ in a hybrid approach